The present invention relates to telecommunications equipment generally, and specifically to methods for securing a cable to an enclosure.
A building entrance protector (BEP) enclosure houses the physical interface between the nodes of a local telecommunications network and a telecommunications cable. For example, a BEP enclosure may house the interface hardware between the telephones of an office building and an exterior telephone cable having a number of twisted copper pairs that carry the voice signals for those telephones. A BEP enclosure is typically mounted in the basement or first floor of the office building. A BEP enclosure may also be used to house the interface hardware for systems based on fiber optical communications. Similarly, BEP enclosures may be used with telecommunications systems carrying signals other than just telephone voice signals.
A BEP enclosure provides two main functions: (1) it houses the hardware that provides connections between a cable and the individual nodes (e.g., telephones) of a local network; and (2) it houses the hardware that provides electrical isolation between the cable and the local network. Electrical isolation is intended to prevent any high voltages and/or high currents that may exist from time to time in the cable from reaching the local network. For example, a BEP enclosure will house isolation components designed to protect telephone users from lightning striking a telephone cable. Such electrical isolation is typically provided by 5-pin plug-in protectors that quickly connect signals to ground upon detection of sufficiently high voltages or currents. Building entrance protectors are described in U.S. Pat. No. 5,803,292 and 5,907,127, which are expressly incorporated by reference herein.
The end cap of a BEP may include one or more cable ports, which extend outwardly from the end cap. The cable port allows the cable to enter into the enclosure. If the BEP is not pressurized, cold shrink tubing is normally used to seal around both the cable and the cable port. Cold shrink tubing is described in U.S. Pat. No. 3,515,798, No. 4,871,599, and No. 5,670,223, all of which are expressly incorporated herein by reference. The cold shrink tubing secures the cable to the BEP housing, aligns the cable, and provides a seal to protect the fiber enclosure from the outdoor environments.
High pressure seals (of greater than about 7 psi) are desirable in enclosures housing optical fibers. If a high-pressure seal is required, cold shrink tubing has not provided a sufficiently air and water tight seal using conventional techniques. To ensure that a high pressure seal is achieved, it is common to inject pressurized air (between five and ten pounds per square inch) into the enclosure to test for leaks. Cold shrink tubing has not been able to provide an adequate seal under these test conditions.
FIGS. 1 and 2 show a conventional cable port 10 having a mounting flange 12, a cylindrical side wall 16 and fasteners 14. FIG. 3 shows a conventional joint 20 using the cable port 10. The cable port 10 is mounted to BEP 30. A cable 50 is secured to the cable port 10 using a cold shrink tubing 40. If the pressure outside the housing 30 is greater than inside the housing, then the outside pressure improves the sealing action of the cold shrink tubing. However, when high pressure is applied inside the BEP housing 30, leakage occurs between the cable and the cold shrink tubing. The high pressure air from the housing 30 can enter between the cable 50 and the tubing 40. Because the pressure of the air inside the tubing 40 is greater than the ambient pressure, leakage develops when the high pressure lifts the tubing away from the cable 50.
In conventional fiber optic enclosures, the cable is typically secured to the housing using a heat shrink tubing. Heat shrink tubing has an adhesive inside it. When heat is applied to the heat shrink tubing, the adhesive melts and the tubing shrinks to grip the cable and cable port.
Heat shrink tubing has several disadvantages. The heat must be applied carefully and uniformly to make the tubing shrink evenly. It takes a long time to heat-treat the heat shrink tubing, often as long as 20 minutes. An expensive heat gun is required. A source of power for the heat gun is also required, which may be inconvenient in the field.
An improved high pressure seal for connecting a cable to a housing is desired.
The present invention provides a method for connecting a cable to a housing. A housing is provided, having a first cable port that extends outward from the housing and a second cable port that extends into the housing. A cable is inserted through the first and second cable ports. A first cold shrink tubing is applied over the first cable port and a portion of the cable that extends outward from the housing. A second cold shrink tubing is applied over the second cable port and a portion of the cable that extends into the housing.
Another aspect of the invention is a device for securing a cable to a housing. The device has first and second cable ports aligned with each other. The device has a mounting flange positioned between the first and second cable ports. The mounting flange is capable of being mounted to a housing, so that the first cable port extends outwardly from the housing, and the second cable port extends into the housing.
Another aspect of the invention is an assembly including a housing having an opening therethrough. The housing has first and second cable ports aligned with the opening and aligned with each other. The first cable port extends outwardly from the housing, and the second cable port extending into the housing. A cable passes through the first and second cable ports. A first cold shrink tubing is placed over the first cable port and a portion of the cable that extends outward from the housing. A second cold shrink tubing is placed over the second cable port and a portion of the cable that extends into the housing.